1. Field of the Invention
The present invention relates to a variable stroke-characteristic engine for a vehicle, including a first link connected to a piston; a second link connected to the first link and a crankshaft; a third link connected at one end to the first link or the second link and movably supported at the other end on an engine block through a control shaft; and an actuator which drives the control shaft.
2. Description of the Related Art
Japanese Patent Application Laid-open Nos. 2004-156537 and 2003-322036 disclose a variable stroke-characteristic engine for a vehicle, having a crankshaft with a main journal rotatably supported in an engine block; a control shaft with a main journal supported for swinging in a predetermined angle range in the engine block; a lower link swingably supported on a pin journal of the crankshaft; an upper link connecting the lower link to a piston; and a control link connecting the lower link to a pin journal of the control shaft, wherein the compression ratio is modified by changing the phase of the control shaft through an actuator to alter the positions of a top dead center and a bottom dead center of the piston.
As described in Japanese Patent Application Laid-open No. 2004-156537, where the actuator connected to an end of the control shaft is disposed on an outer surface of the engine block, if the actuator is located at an exhaust-side portion of the engine block, the high temperature of an exhaust manifold is known to be capable of affecting the durability of the actuator.
Further, as described in Japanese Patent Application Laid-open No. 2003-322036, if the actuator is accommodated on a bottom of the engine block, the influence of the heat from an exhaust gas is avoided. However, in such an arrangement, it is impossible to apply traveling wind to the actuator, which results in a reduction in an amount of heat that is dissipated. Also, the temperature of the actuator is known to rise, which affects the durability of the actuator.